A continuing need exists for adhesives and coatings that have robust adhesion to a variety of different types of substrates. Adhesion to low-surface-tension substrates such as polypropylene, polyethylene, cured ethylene-propylene-diene terpolymer rubber (“EPDM”) or thermoplastic elastomers is particularly problematic. In order to be commercially viable, adhesives and coatings must have certain characteristics in addition to superior bonding strength. Paramount among these characteristics is ease of dispensing from conventional systems, adequate open time, and sufficient shelf life.
In addition, a particular need exists for environmentally acceptable adhesives and coatings that avoid the use of volatile organic solvents. It has thus far been relatively difficult to develop environmentally acceptable adhesives and coatings that perform at a level equal to traditional solvent-based adhesives and coatings. For example, one major problem associated with bonds formed from an aqueous adhesive or coating is the relative susceptibility of the bonds to high temperature fluids and corrosive materials. A further need exists for coatings or adhesives that can be applied with relatively few steps and minimal energy use.
Adhesives used to join large surface area substrates are even more challenging since the adhesive must be able to withstand the exceptionally high stresses and adverse environmental conditions placed on the adhesive joint. Such adhesives are commonly referred to as “structural” adhesives and typically are used to join together two structural members such as metal and plastic substrates in the fabrication, repair and reconstruction of automotive and truck vehicle bodies and component panels and parts such as doors, roofs and hoods.
Metathesis polymers are one class of polymers that have not been exploited commercially in the adhesive or coating fields. Metathesis polymerization of olefin monomers is generally known and typically yields polymers having an unsaturated linear backbone. The degree of unsaturation functionality of the repeat backbone unit of the polymer is the same as that of the monomer. For example, with a norbornene reactant, the resulting polymer should have a structure represented by: Adhesives and coatings are briefly mentioned in a few disclosures pertaining to metathesis polymers.
For example, PCT Patent Application Publication No. WO 97/38036 describes a metathesizable composition that includes a mixture of a thermal carbene-free ruthenium catalyst and a thermal ruthenium carbene catalyst. The polymers resulting from the metathesis polymerization are said to be suitable “as adhesives for bonding substrates having low surface energies (for example Teflon, polyethylene, polypropylene).” The compositions disclosed in WO 97/38036 are also said to be useful as “thermally curable adhesives” and as protective coatings on substrates. However, there is no example of a specific adhesive or coating formulation.
The metathesizable component in the compositions of WO 97/38036 may be a cycloolefin. Various structural formulae for cycloolefins are disclosed that encompass hundreds, if not thousands, of possible cycloolefin compounds. Norbornene per se, norbornene derivatives and norbornadiene are included in the lengthy list of possible cycloolefins, but only norbornene derivatives and polycyclic norbornenes (e.g., dicyclopentadiene) are used in the exemplified embodiments. Similar to the cycloolefin disclosure, WO 97/38036 discloses various structural formulae for each of the catalysts that encompass a myriad number of specific catalyst compounds. One of the possible catalysts is Cl2[P(C6H11)3]2Ru(IV)═CH—C6H5 and it is used in the examples of WO 97/38036 (identified as “catalyst B”). However, these examples all describe using catalyst B and a cycloolefin monomer to make a molded article. Moreover, in comparative examples with catalyst B alone (i.e., it is not mixed with a carbene-free ruthenium catalyst) the disclosed results indicate that the composition incompletely polymerized or produced a soft solid.